How many tidal stations were used as a basis for the National Geodetic Vertical Datum of 1929?

The basis for the National Geodetic Vertical Datum of 1929 (NGVD 29) was established using a network of tidal stations that provided essential measurements for sea level and elevation reference points across the United States. It specifically used a total of 26 tidal stations to obtain precise data. These stations were strategically selected to represent a wide geographical distribution, enabling a more accurate representation of vertical elevations as influenced by the variations in tidal movements.

The selected tidal stations played a crucial role in defining a standard vertical datum that served as a reference for land surveying and engineering projects. By utilizing data from multiple stations, the NGVD 29 incorporated the average sea level measurements, which were critical for establishing a consistent framework for elevation across the nation.